Wired communication network topologies may generally be segmented into two types: Point-to-point and multi-point (also known as ‘point-to-multipoint’, ‘bus’ and ‘shared medium’) networks. In point-to-point topology, the network employs one or more communication links, each link is based on a cable or wires as the communication medium and connects exactly two nodes, wherein each node is connected to an end of the cable. In multipoint configuration, multiple nodes are connected in parallel to the same wired medium is various points along the cable. Non limiting examples of point-to-point based communication networks are Local Area Network (LAN) Ethernet IEEE802.3 10BaseT, 100BaseTX, EIA/TIA-422 (a.k.a. RS-422), ISDN (U-Interface), EIA/TIA-449, IEEE1284, IEEE1394 and USB, and Wide Area Networks (WAN) such as HDSL (High speed Digital Subscriber Line), ADSL (Asymmetric Digital Subscriber Line) and other xDSL technologies (e.g. SHDSL, SDSL, VDSL, IDSL). Non-limiting examples of LANs employing multipoint topology are Ethernet IEEE802.3 10Base2, 10Base5, CAN, LON, and EIA/TIA-485 (a.k.a. RS-485). Other multipoint in-home networks include telephone line based communication such as HomePNA™ (Home Phoneline Networking Alliance), described in www.homepna.org, and powerline based communication such as HomePlug™, described in www.homeplug.org.
A non-limiting example of a unidirectional point-to-point communication link is shown as network 5 in FIG. 1. The network comprises a communication link based on two conductors 11a and 11b cable. A transmitter 14a is connected to one end of the cable at points 7a and 7b. Respective points 6a and 6b at the other end of the cable are connected to a receiver 13a and termination 12a. The signal is coupled to the cable by the transmitter 14a. The signal energy is propagated over the cable and absorbed by the termination 12a, and received by the receiver 13a. 
The term ‘transmitter’ herein includes any device which is capable of outputting energy or driving (or exciting) a signal, including an electrical signal, in a transmission-line. Such devices include line-drivers, modems and transceivers, as well as any other device having excitation capability. Such a signal may either be voltage based, current based or a combination of both. Similarly, the term ‘receiver’ herein includes any device which is able to receive energy/signal (or any function thereof) from a coupled transmission line and convert it to an electrical form, including line receivers, modems and transceivers. Receivers are assumed herein not to include any termination functionality (such as very high input impedance).
A transmission-line is defined as a medium used to carry a signal from a point A to a point B. The terms ‘line’, ‘transmission line’, ‘cable’, ‘wiring’, ‘wire pair’ as used herein should be interpreted to include any type of transmission-line, and specifically a metallic transmission line comprising two or more conductors used to carry electrical signals. Non-limiting examples are coaxial cable, PCB connections and twisted pair, the latter including both UTP (unshielded twisted-pair) and STP (shielded twisted-pair), as well as connections within Application Specific Integrated Circuits (ASTCs). Characteristics of wired transmission-lines and their effect over digital data transmission are described for example in National Semiconductor Corporation Application Note 806 (April 1992) entitled: “Data Transmission Lines and their Characteristics”, and in National Semiconductor Corporation Application Note 808 (March 1992) entitled: “Long Transmission Lines and Data Signal Quality”. Characteristic impedance is a primary property of a metallic transmission line, and commonly relates to the instantaneous voltages and currents of waves traveling along the line.
The basic function of the termination 12a is to fully absorb the signal/energy propagating in the transmission line. Improper termination such as impedance mismatch will cause reflections (a.k.a ringing, overshoot, undershoot, distortion and resonance) back from the receiver-connected end to the transmitter-connected end. Such reflections will commonly degrade the communication characteristics of the communication link. Proper line termination becomes increasingly important as designs migrate towards higher data signal transfer rates over relatively longer lengths or transmission medium. For example, this may be applied to differential data transmission over two conductors such as twisted pair cable. In general, transmission-lines such as cables are treated as transmission-lines when the component wavelengths of the propagating signal, such as an electrical signal in a cable, is shorter than the physical length of the transmission-line. The importance of a proper line termination is discussed for example in National Semiconductor Corporation Application Note 108 (July 1986) entitled: “Transmission Line Characteristics”. A proper line termination typically enables better ability to reliably recover a transmitted signal by using simpler means, as well as improving noise susceptibility.
Analysis of reflections can be found in the National Semiconductor Corporation Application Note 807, (March 1992) entitled: “Reflections: Computations and Waveforms”, and the manner in which reflections impact on data transmission systems is described in the National Semiconductor Corporation Application Note 903 (August 1993) entitled: “A Comparison of Differential Termination Techniques”.
Generally, in order to avoid reflection, the termination impedance should match the characteristic impedance of the transmission line in the frequency band of the discussed signal. If the cable parameters are known, and in particular its characteristic impedance (commonly designated as Z0), a good practice is to install a termination (a.k.a. terminator) 12a of the same value (Z0). In many cases, the cable parameters may be unknown. For example, the cable may exist in a wall and/or be of unknown type. Furthermore, cables may be manufactured with relatively large parameters tolerances, resulting in variations of characteristic impedance from batch to batch. Similarly, the characteristic impedance may change due to environmental conditions such as temperature, humidity and also over time. In any case wherein the cable parameters are not known, a measurement needs to be performed in order to establish the cable characteristic impedance, and accordingly terminating the line. Such measurement requires expertise, is labor extensive and time consuming.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method and system for allowing easy and simple measuring of characteristic impedance, upon which a proper termination of a transmission line may be calculated, for example. Such system may be applied to transmission lines in general, and wired networks in particular, and specifically for a metallic transmission line having an unknown or changing characteristic impedance.
A multi-point based network (a.k.a. bus or multidrop network) is shown as network 10 in FIG. 1a. Two conductors 11a and 11b are used as the communication medium, wherein multiple nodes are connected thereto, each node connected at a distinct point along the line. The network is shown in a state wherein node 14a connected to the two conductors 11a and 11b of the line at respective connection points 18a and 18b is a transmitter, while all other nodes serve as receivers. Nodes 13a, 13b and 13c serve as receivers and are connected to the line at respective points (17a, 17b), (19a, 19b) and (9a, 9b) respectively. Similar to the above discussion, a termination (equal to the line characteristic impedance) is connected to each end, wherein terminations 12a and 12b are respectively connected to the transmission line ends (15a, 15b) and (16a, 16b).
Typically in wired communication, the wiring characteristic impedance is near pure resistance (non-complex impedance); hence each termination could be a simple resistor having a resistance equal to the characteristic impedance. Such resistors 23 are shown as terminations and are connected to the transmission line end points (such as 16a, 16b) of network 20 shown in FIG. 2.
While the metallic transmission line 5 shown in FIG. 1 is a non-tapped, single-path, homogenous and continuous wiring, a transmission line may sometimes involves a tap (a.k.a stub, bridge, and bridge-tap) or any other discontinuity. Such medium is shown in FIG. 2 as network 20. In addition to the two conductors 11a and 11b, the network employs an additional wiring part (a tap) comprising two conductors 21a and 21b, tapped in connection points 22a and 22b respectively. Similar to the above discussion, a termination is required in each line end, hence requiring resistor 23c connected across the tap end points 24a and 24b. Similarly, a wired network may employ multiple such taps. Hence for a line having arbitrary topology such as ‘star’, ‘tree’ or any combination thereof, the taps may be without any node connection (such as shown in network 20), or may have nodes connected thereto. In addition, nodes may be connected to one or more of the line ends, in parallel to the termination.
In a multi-point environment, while termination is essential in all wiring ends in order to reduce reflections, it is equally important not to introduce termination at all points other than the cable ends. Any impedance connected will cause a mismatch and a signal propagated will introduce reflections at that point. As such, the nodes 13a, 13b and 13c should exhibit high impedance in their connection points to the transmission line.
In many cases, nodes (in particular receivers) comprise a built-in termination/resistor. If the node is connected in one of the line ends, the termination should be connected in parallel to the node. However, in a configuration wherein the node is not located in the line ends, the termination should be disconnected or disabled, in order to avoid generation of reflections. Such distinction between the connection locations complicates the network installation. Furthermore, in some cases the wiring topology is not easily known, such as in the case of in-wall existing wiring. Identifying the topology in order to distinguish between line ends and other points may be complex, labor intensive and expensive.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method and system for allowing easy and simple termination of a transmission line in general, and wired networks in particular, and specifically for a metallic transmission line having multiple connection points, unknown to be either ends or in the middle of a wiring system.
Wired Home Networking.
Most existing offices and some of the newly built buildings facilitate a data network structure based on dedicated wiring. However, implementing such a network in existing buildings typically requires installation of new wiring infrastructure. Such installation of new wiring may be impractical, expensive and problematic. As a result, many technologies (referred to as “no new wires” technologies) have been proposed in order to facilitate a LAN in a building without adding new wiring. Some of these techniques use existing utility wiring installed primarily for other purposes such as telephone, electricity, cable television (CATV), and so forth. Such an approach offers the advantage of being able to install such systems and networks without the additional and often substantial cost of installing separate wiring within the building.
The technical aspect for allowing the wiring to carry both the service (such as telephony, electricity and CATV) and the data communication signal commonly involves using FDM technique (Frequency Division Multiplexing). In such configuration, the service signal and the data communication signals are carried across the respective utility wiring each using a distinct frequency spectrum band. The concept of FDM is known in the art, and provides means of splitting the bandwidth carried by a medium such as wiring. In the case of telephone wiring carrying both telephony and data communication signals, the frequency spectrum is split into a low-frequency band capable of carrying an analog telephony signal and a high-frequency band capable of carrying data communication or other signals.
A network in a house based on using powerline-based home network is also known in the art. The medium for networking is the in-house power lines, which is used for carrying both the mains power and the data communication signals. A PLC (Power Line Carrier) modem converts a data communication signal (such as Ethernet IEEE802.3) to a signal which can be carried over the power lines, without affecting and being affected by the power signal available over those wires. A consortium named HomePlug Powerline Alliance, Inc. of San Ramon, Calif. USA is active in standardizing powerline technologies. A powerline communication system is described in U.S. Pat. No. 6,243,571 to Bullock et al., which also provides a comprehensive list of prior art publications referring to powerline technology and application. An example of such PLC modem housed as a snap-on module is HomePlug1.0 based Ethernet-to-Powerline Bridge model DHP-100 from D-Link® Systems. Inc. of Irvine, Calif., USA. Outlets with built in PLC modems for use with combined data and power using powerlines are described in US Patent Application 2003/0062990 to Schaeffer et al. entitled ‘Powerline bridge apparatus’. Such power outlets are available as part of PlugLAN™ by Asoka USA Corporation of San Carlos, Calif. USA.
Similarly, carrying data over existing in home CATV coaxial cabling is also known in the art, for example in US Patent application 2002/0166124 to Gurantz et al. An example of home networking over CATV coaxial cables using outlets is described in US Patent application 2002/0194383 to Cohen et al. Such outlets are available as part of HomeRAN™ system from TMT Ltd. of Jerusalem, Israel.
Telephony Definitions and Background
The term “telephony” herein denotes in general any kind of telephone service, including analog and digital service, such as Integrated Services Digital Network (ISDN).
Analog telephony, popularly known as “Plain Old Telephone Service” (“POTS”) has been in existence for over 100 years, and is well designed and well engineered for the transmission and switching of voice signals in the 300-3400 Hz portion (or “voice band” or “telephone band”) of the audio spectrum. The familiar POTS network supports real-time, low-latency, high-reliability, moderate-fidelity voice telephony, and is capable of establishing a session between two end-points, each using an analog telephone set.
The terms “telephone”, “telephone set”, and “telephone device” herein denote any apparatus, without limitation, which can connect to a Public Switch Telephone Network (“PSTN”), including apparatus for both analog and digital telephony, non-limiting examples of which are analog telephones, digital telephones, facsimile (“fax”) machines, automatic telephone answering machines, voice (a.k.a. dial-up) modems, and data modems.
The terms “data unit”, “computer” and “personal computer” (“PC”) are used herein interchangeably to include workstations, Personal Digital Assistants (PDA) and other data terminal equipment (DTE) with interfaces for connection to a local area network, as well as any other functional unit of a data station that serves as a data source or a data sink (or both).
In-home telephone service usually employs two or four wires, to which telephone sets are connected via telephone outlets.
Home Networking Existing in-House Wiring.
Similarly to the powerlines and CATV cabling described above, it is often desirable to use existing telephone wiring simultaneously for both telephony and data networking. In this way, establishing a new local area network in a home or other building is simplified, because there is no need to install additional wiring. Using FDM technique to carry video over active residential telephone wiring is disclosed by U.S. Pat. No. 5,010,399 to Goodman et al. and U.S. Pat. No. 5,621,455 to Rogers et al.
Existing products for carrying data digitally over residential telephone wiring concurrently with active telephone service by using FDM commonly uses a technology known as HomePNA (Home Phoneline Networking Alliance) whose phonelines interface has been standardized as ITU-T (ITU Telecommunication Standardization Sector) recommendation G.989.1. The HomePNA technology is described in U.S. Pat. No. 6,069,899 to Foley, U.S. Pat. No. 5,896,443 to Dichter, U.S. Patent application 2002/0019966 to Yagil et al., U.S. Patent application 2003/0139151 to Lifshitz et al. and others. The available bandwidth over the wiring is split into a low-frequency band capable of carrying an analog telephony signal (POTS), and a high-frequency band is allocated for carrying data communication signals. In such FDM based configuration, telephony is not affected, while a data communication capability is provided over existing telephone wiring within a home.
Outlets
The term “outlet” herein denotes an electro-mechanical device, which facilitates easy, rapid connection and disconnection of external devices to and from wiring installed within a building. An outlet commonly has a fixed connection to the wiring, and permits the easy connection of external devices as desired, commonly by means of an integrated standard connector in a faceplate. The outlet is normally mechanically attached to, or mounted in, a wall or similar surface. Non-limiting examples of common outlets include: telephone outlets for connecting telephones and related devices; CATV outlets for connecting television sets, VCR's, and the like; outlets used as part of LAN wiring (a.k.a. structured wiring) and electrical outlets for connecting power to electrical appliances. The term “wall” herein denotes any interior or exterior surface of a building, including, but not limited to ceilings and floors, in addition to vertical walls.
Functional Outlet Approach.
This approach involves substituting the existing service outlets with ‘network’ active outlets. Outlets in general (to include LAN structured wiring, electrical power outlets, telephone outlets, and cable television outlets) have evolved as passive devices being part of the wiring system house infrastructure and solely serving the purpose of providing access to the in-wall wiring. However, there is a trend towards embedding active circuitry in the outlet in order to use them as part of the home/office network, and typically to provide a standard data communication interface. In most cases, the circuits added serve the purpose of adding data interface connectivity to the outlet, added to its basic passive connectivity function.
An outlet supporting both telephony and data interfaces for use with telephone wiring is disclosed in U.S. Pat. No. 6,549,616 entitled ‘Telephone outlet for implementing a local area network over telephone lines and a local area network using such outlets’ to Binder. Such outlets are available as part of NetHome™ system from SercoNet Ltd. of Ra'ananna, Israel.
Another telephone outlet is described in U.S. Pat. No. 6,216,160 to Dichter, entitled ‘Automatically configurable computer network’. An example of home networking over CATV coaxial cables using outlets is described in WO 02/065229 published 22 Aug. 2002 entitled: ‘Cableran Networking over Coaxial Cables’ to Cohen et al. Such outlets are available as part of HomeRAN™ system from TMT Ltd. of Jerusalem, Israel. Outlets for use in conjunction with wiring carrying telephony, data and entertainment signals are disclosed in US Patent Application US2003/0099228 to Alcock entitled ‘Local area and multimedia network using radio frequency and coaxial cable’. Outlets for use with combined data and power using powerlines are described in US Patent Application US2003/0062990 to Schaeffer et al. entitled ‘Powerline bridge apparatus’. Such power outlets are available as part of PlugLAN™ by Asoka USA Corporation of San Carlos, Calif. USA.
While the active outlets have been described above with regard to networks formed over wiring used for basic services (e.g. telephone, CATV and power), it will be appreciated that the invention can be equally applied to outlets used in networks using dedicated wiring. In such a case, the outlet circuitry is used to provide additional interfaces to an outlet, beyond the basic service of single data connectivity interface. For example, it may be used to provide multiple data interfaces wherein the wiring supports single such data connection. An example of such outlet is the Network Jack™ product family manufactured by 3Com™ of Santa-Clara, Calif., U.S.A. In addition, such outlets are described in U.S. Pat. No. 6,108,331 to Thompson entitled ‘Single Medium Wiring Scheme for Multiple Signal Distribution in Building and Access Port Therefor’ as well as U.S. Patent Application US 2003/0112965 Published Jun. 19, 2003 to McNamara et al. entitled ‘Active Wall Outlet’.
While the active outlets have been described with regard to outlets and networks based on conductive media such as wires and cables, it will be appreciated that such outlets are equally applicable in the case wherein the network medium is non-conductive, such as fiber-optical cabling. Active outlets supporting data interfaces and based on fiber optic cabling are described in U.S. Patent Application US 2002/0146207 Published Oct. 10, 2002 to Chu, entitled ‘Fiber Converter Faceplate Outlet’, as well as in U.S. Pat. No. 6,108,331 to Thompson entitled ‘Single Medium Wiring Scheme for Multiple Signal Distribution in Building and Access Port Therefor’. As such, the term ‘wiring’ as used in this application as well as in the appended claims should be interpreted to include networks based on non-conductive media such as fiber-optics cabling.
While the outlets described above use active circuitry for splitting the data and service signals, passive implementations are also available. An example of such a passive outlet is disclosed in WO 02/25920 to Binder entitled ‘Telephone communication system and method over local area network wiring’. Such outlets are available as part of the etherSPLIT system from QLynk Communication Inc. of College Station, Tex. USA. etherSPLIT is a registered trademark of Dynamic Information Systems.
The described above outlets are complete and self-contained devices. As such, they can be easily installed in new houses instead of regular passive simple outlets. However, such solutions are not appropriate in the case of retrofitting existing wiring systems. In most cases, any such modification will require dismantling the existing outlets and installing the new ones having the improved features. Such activity is cumbersome, expensive and will often require professional skill. Furthermore, owing to safety aspects involved while handling hazardous voltages (such as in the powerlines and telephone lines), local regulations may require only certified personnel to handle the wiring, making it expensive and militating against a do-it-yourself approach.
Furthermore, as the technology and environment change in time, a need to upgrade, modify or change the outlet functionalities, features and characteristics may arise. For example, the data interface may need to be upgraded to interconnect with new standards. In another example, the circuitry may need to be upgraded to support higher bandwidth. Similarly, management and Quality of Service (QoS) functionalities may need to be either introduced or upgraded. In yet other examples, additional functionalities and interfaces may need to be added. Using complete self-contained outlets as a substitute to the existing ones also introduces the disadvantages described above.
Plug-in Device.
One approach to adding functionality to existing outlets is by using a plug-in module. Such plug-in modules are described in US Patent Application US 2002/0039388 to Smart et al entitled ‘High data-rate powerline network system and method’. US Patent Application US 2002/0060617 to Walbeck et al. entitled ‘Modular power line network adapter’ and also in US Patent Application US 2003/0062990 to Schaeffer, JR et al. entitled ‘Powerline bridge apparatus’. Such a module using HomePlug™ technology are available from multiple sources such as part of PlugLink™ products by Asoka USA Corporation of San Carlos, Calif., USA. HomePlug is a trademark of HomePlug Powerline Alliance, Inc. of San Ramon, Calif., USA. Various types of snap-on devices are also described in WO 04/001034.